Thermal curing methods and systems for forming contact lenses

Abstract

Contact lens curing systems and methods are described. A contact lens curing system includes an oven that has a plurality of curing zones, a mold advancement system for moving the contact lens mold assemblies between the plurality of zones, and a controlled atmosphere within the curing zones that provides a substantially chemically inert environment in which contact lens precursor materials can be polymerized in contact lens mold assemblies located in the curing zones. Methods of producing contact lenses include curing contact lens precursor materials in contact lens mold assemblies in the lens curing system. As an example, an oven for curing contact precursor materials in molds, the curing process being done in an inert atmosphere, includes a plurality of heating zones, such as three heating zones 106, 107, 108 or two heating zones 307, 308 and a mold advancement system for moving the molds between the plurality of zones, wherein a first zone and second zone of the plurality of zones are maintained at different temperatures 106, 107 or 307, 308.

1. A method of forming contact lenses by curing contact lens precursor materials in molds, wherein the method comprises the following steps:
 providing amounts of a contact lens precursor material in molds of a first mold stack, 
 providing an oven, 
 providing an inert atmosphere in the oven, and 
 heating the molds in the oven to cure the contact lens precursor material in the molds by:
 moving gas flow over a heating element and through the oven; and 
 moving the molds between a plurality of zones that are defined at least partially by at least one wall; and 
 
 wherein the oven is operable to maintain simultaneously a first zone of the plurality of zones at a first temperature and a second zone of the plurality of zones at a second, different, temperature. 
 
     
     
       2. A method as claimed in  claim 1 , further comprising rotating a fan to discharge gas flow over a heating element. 
     
     
       3. A method as claimed in  claim 1 , further comprising directing the gas flow through a discharge duct and passing the gas flow through the oven. 
     
     
       4. A method as claimed in  claim 2 , further comprising directing the gas flow through a return duct and into an inlet end of the fan. 
     
     
       5. A method as claimed in  claim 1 , further comprising the step of restricting heat flow between the first zone and the second zone. 
     
     
       6. A method as claimed in  claim 1 , further comprising adjusting an opening to restrict the gas flow in a discharge duct. 
     
     
       7. A method as claimed in  claim 1 , further comprising the step of stopping the molds within the first zone or the second zone or both the first zone and the second zone. 
     
     
       8. A method as claimed in  claim 1 , further comprising moving molds of a second mold stack through the oven. 
     
     
       9. A method as claimed in  claim 1 , further comprising using a perforated plate for restricting the gas flow. 
     
     
       10. A method as claimed in  claim 1 , wherein each of the plurality of zones is defined by a different oven chamber, the chambers being in sufficient communication with each other for the molds to be moved between them. 
     
     
       11. A method as claimed in  claim 1 , wherein the oven comprising the plurality of zones is in the form of a super-oven comprising a plurality of sub-ovens, and each sub-oven defines at least one of said plurality of zones. 
     
     
       12. A method as claimed in  claim 1 , wherein a moveable wall defines at least part of a boundary between two of the plurality of zones. 
     
     
       13. A method as claimed in  claim 1 , wherein a stationary wall defines at least part of a boundary between two of the plurality of zones. 
     
     
       14. A method as claimed in  claim 1 , wherein the plurality of zones are in gas communication with each other, so that the inert atmosphere is a single inert atmosphere, extending throughout the plurality of zones. 
     
     
       15. A method as claimed in  claim 1 , wherein the oven includes a scrubber for scrubbing volatile materials from the inert atmosphere. 
     
     
       16. A method as claimed in  claim 1 , wherein the oven comprises an entrance chamber and the mold advancement system is arranged to move the molds from the entrance chamber into one zone of the plurality of zones. 
     
     
       17. A method as claimed in  claim 16 , wherein the oven comprises an automated placement device arranged to put the molds into the entrance chamber. 
     
     
       18. A method as claimed in  claim 17 , wherein the oven comprises an exit chamber and the mold advancement system is arranged to move the molds from one zone of the plurality of zones into the exit chamber. 
     
     
       19. A method as claimed in  claim 18 , wherein the oven comprises an automated placement device arranged to remove the molds from the exit chamber. 
     
     
       20. A method as claimed in  claim 18 , wherein the entrance and exit chambers are the same chamber. 
     
     
       21. A method as claimed in  claim 1 , wherein the oven includes a plurality of transport units for supporting the molds. 
     
     
       22. A method as claimed in  claim 21 , wherein at least one of the transport units includes a baffle portion arranged to form at least part of a zone wall, so that when the transport unit is in one of the zones, the zone wall acts to restrict heat flow into an adjacent zone. 
     
     
       23. A method as claimed in  claim 22 , wherein each transport unit includes a baffle portion and the baffle portion of one of the transport units is arranged to co-operate with a corresponding baffle portion on another transport unit to form at least part of a zone wall. 
     
     
       24. A method as claimed in  claim 21 , wherein at least some of the transport units are stacked vertically. 
     
     
       25. A method as claimed in  claim 21 , wherein at least two of said plurality of transport units include couplings that couple together the two transport units to form at least part of a train of said transport units.